This invention relates generally to welding and more particularly to a method of welding a roof panel to a rear quarter panel of an automotive vehicle.
In a typical welding operation to secure the roof panel to the rear quarter panel of an automotive vehicle, it is customary to offset an edge portion of one of the panels to form a shoulder, place the other panel over the offset edge portion of the first panel with an edge of the second panel adjacent to the shoulder of the first panel to provide a joint, and then to apply resistance spot welds to the overlapping edge portions prior to applying a continuous weld along the joint by gas-metal arc welding sometimes referred to as metal inert gas (MIG) welding. MIG welding is a process in which the heat for welding is generated by an arc between a consumable electrode and the work metal. The electrode, a bare solid wire that is continuously fed to the weld area, becomes the filler material as it is consumed. The electrode, weld puddle, arc and adjacent areas of the base metal are protected from atmospheric contamination by a gaseous shield provided by a stream of gas, or mixture of gases, fed through the electrode holder. The gas shield must provide full protection, because even a small amount of entrained air can contaminate the weld deposit.
There are several problems with this method of securing the two panels together, relating particularly to the formation of resistance spot welds. A resistance spot welder has two electrodes with contact tips attached to each. These contact tips are closed onto the metal and pressure is applied usually by a pneumatic cylinder. Once the contact tips are closed onto the metal, a low voltage is applied which causes a high current to be generated due to the low resistance between the contact tips. This current melts the metal at the point of contact and a weld is produced. Under ideal conditions, any one of several problems can cause deficiencies in the spot welds.
These problems could be any one of, but not limited to, the following:
Incorrect voltage;
Incorrect duration of time voltage is applied;
Incorrect pressure applied;
Misalignment of contact tips causing panel distortion;
Contact tip wear;
Contamination of a contact tip from sealer or paint;
Indentation of the metal at the point of contact.
Any of these conditions will cause problems with the weld, but even a perfect resistance weld will leave a blemish on one or both outer surfaces of the metal being welded.
It has been proposed to simply eliminate the spot welding. However, this leaves the joint unsecured over its length as the continuous MIG weld is applied to the joint. The joint opens up forming a gap between the two overlapping panels into which the MIG weld material can seep resulting in high spots and low spots in the overlapping panels and requiring much additional work to form a finished joint.
The resistance spot welds must be made in the overlapping material at points spaced from the joint, in order for the welds to be formed correctly. If the weld is located on or close to the edge of one of the panels, metal is expelled from between the panels as the molten metal pool is formed. This expulsion of metal causes a very poor weld to be formed because most of the metal pool which would normally form the weld xe2x80x9cnuggetxe2x80x9d on cooling is no longer present.
Resistance spot welds are not used in the present invention. Instead, MIG spot welds are applied at spaced points along the joint. In order to hold the overlapping panels tightly together, pressure is applied by a pressure applicator adjacent to each MIG spot weld as it is being formed. The pressure applicator moves along with the MIG welding gun to apply pressure during the formation of each MIG spot weld. After the panels are secured together by the MIG spot welds, linear MIG weld segments are applied between the spot welds to form a continuous line of MIG welding along the joint. The panels are held tightly together by the MIG spot welds during the application of the MIG weld segments so that welding material will not seep between the panels.
One object of this invention is to provide a method of welding having the foregoing features and capabilities.
Other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying claims and drawings.